Voice of the DBA

Tag: T-SQL Tuesday

Catch up with T-SQL Tuesday

T-SQL Tuesday is a monthly blog party where we get an invitation the first week of the month to write on a specific topic for the second Tuesday of that month. Adam Machanic came up with the idea and he chooses the hosts.

If you’re interested in hosting, contact him.

While there’s a sense of community and participation here, and certainly the chance to showcase some of your knowledge for others, it’s also got another benefit.

It’s the chance for you to learn something.

Not by reading other’s posts, but by writing your own. This is your opportunity to bolster your own skills, and teach yourself something new.

Don’t Worry About Timing

I know many of you are worried about the pressure of producing something good. I know many of you will find that the first weekend of the month is really busy and you can’t write.

That’s fine.

I’ve got a list of all previous invitations and topics. Go back and pick one of them and write your own post today. Start working on it, teach yourself something, and put some thoughts down. Research what others have done by looking through the roundups. Get a friend to review the work and see if it’s readable and makes sense.

Do that ten times. It might take you ten months, but I’m sure you can write something down about SQL Server once a month.

When you get ten, start a blog and publish them. Use the T-SQL Tuesday tag, but I’d also encourage you to use the #SQLNewBlogger tag as well. Start showing your boss that you’re improving your skills. Be ready to impress you potential next new boss with a series of posts on SQL topics.

Your career will be better off, and the world will start to see better software being written.

Start improving your skills this weekend, or start documenting the learning you already do. Either way, start building a better brand for your career.

August 14, 2015
T-SQL Tuesday #69–Encryption
This is a good T-SQL Tuesday topic for me. This month Ken Wilson asks everyone to write on encryption, which is a topic I’ve presented on quite a few times.

You can participate, too. Take a few hours, learn something, and tell us what you learned. Let everyone know how you view this topic and grow your blog with a little new knowledge.

T-SQL Tuesday is a great chance to force you to write a post on a specific topic. Your post needs to publish on the second Tuesday of the month, Aug 11 this month, to be included in the roundup from the host. However feel free to write about this topic anytime, and even include the T-SQL Tuesday title.

CASTing Results

A short post this month, as I’m a bit buried in a few things, but this is one of those encryption notes that I didn’t see well documented when I started working with the subject, and I’m hoping I can save you a few minutes of frustration.

If you encrypt your data, it will be stored as a binary type. This is because encrypted data is supposed to be random, and not easily decrypted.

Let’s imagine I have some simple setup like the code below. I’ll create a key, open it, and use it to encrypt some data that I’ll insert into a table.
```
CREATE TABLE MyEncryptionTest( intsource INT, charsource VARCHAR(50), intencrypt VARBINARY(max), charencrypt VARBINARY(max));
CREATE SYMMETRIC KEY Mykey WITH    ALGORITHM = AES_128 ENCRYPTION BY PASSWORD = 'M$test78';
GO
OPEN SYMMETRIC KEY MyKey DECRYPTION BY PASSWORD = 'M$test78';

INSERT dbo.MyEncryptionTest
        ( intsource ,
          charsource ,
          intencrypt ,
          charencrypt
        )
VALUES  ( 7, 
          'Spike' , 
          ENCRYPTBYKEY(KEY_GUID('MyKey'), CAST(7 AS VARCHAR(10))) ,
          ENCRYPTBYKEY(KEY_GUID('MyKey'), 'Spike')
        );

SELECT top 20
 * FROM dbo.MyEncryptionTest;
```
The results of this are that I get binary data:

Now, the decryption routine for T-SQL doesn’t need to specify the key. That means instead of a *, I can use the DECRYPTBYKEY function and pass in the column.
```
SELECT TOP 20
        intdecrypt = DECRYPTBYKEY(intencrypt),
        chardecrypt = DECRYPTBYKEY(charencrypt) ,
        intencrypt ,
        charencrypt
FROM    dbo.MyEncryptionTest;
```
This gives me this:

Not quite what I want. What if I cast this back to an integer? After all, the output of the function is listed as an nvarchar.
```
SELECT TOP 20
        intdecrypt = CAST(DECRYPTBYKEY(intencrypt) AS INT),
        chardecrypt = DECRYPTBYKEY(charencrypt) ,
        intencrypt ,
        charencrypt
FROM    dbo.MyEncryptionTest;
```
I see:

Again, not what I wanted. However, since I know something about conversions, I realize the output is close to what I want. In fact, what I need to do is perform a different CAST before I perform my final one. Here I’ll decrypt the results as NVARCHAR first, then as an INT.
```
SELECT TOP 20
        intdecrypt = CAST(CAST(DECRYPTBYKEY(intencrypt) AS NVARCHAR(30)) AS INT),
        chardecrypt = DECRYPTBYKEY(charencrypt) ,
        intencrypt ,
        charencrypt
FROM    dbo.MyEncryptionTest;
```
Now I see:

If I do the same for the character column:
```
SELECT TOP 20
        intdecrypt = CAST(CAST(DECRYPTBYKEY(intencrypt) AS NVARCHAR(30)) AS INT),
        chardecrypt = CAST( DECRYPTBYKEY(charencrypt) AS VARCHAR(50)) ,
        intencrypt ,
        charencrypt
FROM    dbo.MyEncryptionTest;
```
I’ll get the correct results.

Note that if I take the character column and cast to nvarchar, I’ll get something different. Try it and see.

And don’t forget to close your key.
```
CLOSE SYMMETRIC KEY mykey;
```
August 11, 2015
No Defaults – T-SQL Tuesday #68

It’s the second Tuesday of the month, and time for T-SQL Tuesday. This month’s invitation is from Andy Yun, where he asks you to Just Say No to Defaults.

This is the monthly blog party started by Adam Machanic, and it’s the chance for you to write on a particular topic every month. The hosts rotate, so you have to watch the #tsql2sday hashtag for the topic. Posts for the month need to go live during the day according to UTC time.

I also keep a list of topics on the blog here, and you should feel free to write about any past topics and post something on your blog. It’s great practice, and a good way to get started as a #SQLNewBlogger.

Default Changes

There are all sorts of defaults in SQL Server. The setup program presents you with a number of choices, but in most cases a default exists for setting because SQL Server needs something.

I used to have a setup script that I would run for every new install. In a few jobs, back when we used to have physical servers, a hardware person or sysadmin would install Windows and SQL Server onto a new computer and then send me the name for customization. My script, which was really a series of SQLCMD calls in a batch file that in turn called various other scripts, was designed to add an administrative database, create some jobs to track the system, setup backups, and more.

The process really did part of what Policy Based Management can do, but was simpler and tailored to ensure that all of our SQL Servers worked in a similar manner. We could override settings, but this quick script gave us a starting point that all DBAs understood. We even ran this on development machines for instances we didn’t manage as it allowed us to troubleshoot other issues, it only took a few minutes, and it removed some of the management headaches from the developers’ minds.

However, there is one thing I’ve almost always changed on my instances. I try to do it during setup, but at times I need to do it later. That setting is the default location for files. I do this as I want to usually have data files, log files, and backup files separate from each other.

Even if I don’t have different drives, but setting up separate locations here now, I can easily move the files later and make one change here for the defaults and I know I’ll have things separate.

I’m not running a new install this week, but I’ll show you how to change it on an instance that’s installed. First, right click the instance in Object Explorer and click Properties.

Next, go to the Database Settings section.

At the bottom here you see locations for data, log, and backup. In this case, on my laptop, I only have two drives, so I can’t achieve great separation.

However in any production system, I’d have the data and logs separated to different physical drives, or at least different LUNs. Backups might go with logs, but they’d ideally be separated to another location.

July 14, 2015
T-SQL Tuesday #67 – Extended Events for DBCC

It’s the second Tuesday of the month and time for another T-SQL Tuesday. This time it’s #67 from Jes Borland on Extended Events. You can read the invite, and whether you can participate today or not, write your blog and leave a comment for Jes on her blog.

If you want to see all the topics from the past, I have them on a post here.

If you want to host, contact the founder of T-SQL Tuesday, Adam Machanic. He chooses the hosts and is always looking for people that want to participate. You just need a blog and a good idea.

Who Ran DBCC?

I ran across a question recently from someone that said DBCC messages had appeared in the error log, but no one had run DBCC. That’s not possible as DBCC isn’t run without someone, whether that’s a human or a service, executing the DBCC command.

In the past, I might recommend a trace to track this, but not I’d choose an Extended Events (XE) session. I’ll show how to set up a simple session, though be aware I’m not an XE guru. I’m sure there are better ways to structure this, but it worked well for me.

You can start quickly building a specific XE session by right clicking the Sessions folder under Extended Events in SSMS under Management. I tend to pick the wizard for getting started, though be sure to save the script later.

From here we get the opening screen for XE, which I won’t show. The next screen asks for a name for the session. It doesn’t matter, but once you start using XE, you’ll start to get quite a few session, so it’s handy to pick something that’s simple and easy to understand later.

I can choose to start the session here when I’m done, but don’t worry if you’re not sure. You’ll get a chance again later.

The next step is to decide whether you use a template or build a session from scratch. I’m not sure if any of these templates will work well as I haven’t dug in. In my case, I decided to just choose a generic session.

Now I need to pick the events. There are a lot, but I went down to get the sql_statement_completed as my event. This will let me see the text of a call, which is what I need.

A couple notes here. One, you might want to grow this screen so that you can read what’s in the lower windows. I know there’s a lot of data here, but this screen doesn’t seem well defined.

The second note is that don’t forget to add the event with the arrow button. Until you have an event (or multiple events) in the right window, you can’t click "Next".

The next step is to get the data fields you need. Again, there are a lot, and I limited this to what I needed. I grabbed the client host and app, as well as the database. Then I grabbed the service_principal_name and sql_text as well. This should let me determine who’s running the command.

I’ve got lots of data here, but I only care about the execution of dbcc checkdb. This means I need to filter things, which is my choice with the next screen.

Here I need to click in the top line to get a place to add a filter. Then I select sql_text from the drop down and choose like for the operator and "dbcc checkdb" for the value. This should grab events that execute with a dbcc call.

I have to choose where to store this data. Since this is mostly a check for me, I can just use the ring buffer and keep data in memory. I lowered this to 10 events, but you can certainly pick what works for you. If you care about auditing, drop this in a file. For a small session like this, there’s not much data that’s going to be captured.

I get a summary screen, which lets me review settings. I haven’t shown it here, but once I pass that, I get the "Success" screen. This is where I can start the session, and actually watch live data if I want.

For this, I’ll watch the live data.

I decided to test this first and see if it captures anything else. I ran a few queries, and then this:

Still a blank, live data screen. Then I ran checkdb. I saw the results, and then ran it a few more times.

As you can see, I now can see that I ran checkdb against the EncryptionPrimer database.

This lets me do some quick auditing of what’s happening with my DBCCs. A smart DBA might even use this to ensure that DBCC is being run against some databases, perhaps on a spare machine.

June 9, 2015